1. Field of the Invention
The present invention relates to an antenna apparatus. More particularly, the present invention relates to an antenna apparatus which is used in a radar or the like for transmitting and receiving an electromagnetic wave of a millimetric-wave band and a transmission and receiving apparatus using the same.
2. Description of the Related Art
Millimetric-wave radars to be mounted in motor vehicles are used in a system for supporting safe driving of automobiles. The millimetric-wave radar is used to measure the distance between two automobiles or between an obstacle in the path of an automobile and the automobile. Based on the measurement data, the speed control and braking of the automobile are performed so that collision into another automobile or an obstacle is prevented.
Generally, a transmission and receiving module using a millimetric-wave radar incorporates a millimetric-wave oscillator, a circulator, a directional coupler, a mixer, an antenna, and so on.
The vehicle on the right side in FIG. 21 (behind) radiates a millimetric wave from a radar by an FM-CW (Frequency Modulation-Continuous Wave) method to the automobile on the left side (ahead) and receives a millimetric wave reflected by the automobile on the left side. The distance between the right and left automobiles and the relative speed between the right and left automobiles are computed by a known computation method.
The computation is performed by a signal processing section of the signal processing apparatus of FIG. 22. The result of the computation is transmitted to a control and warning section. The control and warning section causes a warning device to operate when, for example, the driving velocity of the automobile on the right is equal to or higher than a predetermined value and the distance between the right and left automobiles is equal to or lower than a predetermined value. Alternatively, the control section may operate a braking apparatus of the right or trailing automobile under given conditions.
Since the directivity of the antenna used in the conventional millimetric-wave radar is fixed, problems such as those described below occur.
As shown in FIG. 18, when separate automobiles are driving on two parallel traffic lanes, a millimetric wave transmitted from a radar of an automobile Cm may reach an automobile Ca and an automobile Cb in front. This is because adjustments cannot be made such that the directivity of the antenna is varied so that the millimetric wave is radiated only to the automobile within the traffic lane in which the automobile Cm is driving.
The millimetric wave which reaches the respective automobiles is reflected and received by the automobile Cm. Since the automobiles Cb and Cm are driving in separate traffic lanes, even if the automobiles Cb and Cm come too close to each other, the automobile Cm does not need to perform special safety control.
However, in the automobile Cm, it is not possible to identify from which automobile Ca or Cb the received wave has been reflected. Therefore, when the vehicle-to-vehicle distance between the automobiles Cb and Cm is smaller than an allowable distance, control for safety is performed by the automobile Cm. Further, when the directivity of the antenna is fixed, inconveniences such as those described below occur.
An automobile Cm driving near the entrance of a curve in FIG. 19 radiates a millimetric wave B1; however, the millimetric wave does not reach the automobile Ca driving near the exit of the curve.
Also in the case where a road has inclines and declines, as shown in FIG. 20, in the automobile Cm driving before a slope while radiating the millimetric wave B1, the automobile Ca moving on the slope is not detected.
Therefore, the following method may be used in which the direction of a radiation beam is changed to solve the above-described problems.
For example, in FIG. 18, radiation beams B1, B2, and B3 are radiated respectively so as to make measurements for each direction. By comparing these results, it is possible to detect the automobiles Ca and Cb individually.
In the example shown in FIG. 19, the presence of a curve in front of the automobile Cm is recognized based on the steering-wheel operation, and the millimetric wave B1 is switched to the millimetric wave B2. There is also a method for detecting a curve by analyzing the image input from a camera. Also in the example shown in FIG. 20, a slope is detected by analyzing the image input from the camera, and the millimetric wave B1 is switched to the millimetric wave B2.
In the conventional radar system, the direction of radiation of a radiation beam of an electromagnetic wave is changed by rotating the housing of the transmission and receiving apparatus which incorporates an antenna by a motor or the like. Since the housing includes parts other than the antenna, it is difficult to reduce the size of the mechanism for rotating the housing. Therefore, it is difficult to rotate the housing at a high speed and to scan the radiation beam at a high speed.
An object of the present invention is provide an antenna apparatus and a transmission and receiving apparatus using the same having a small size and being capable of switching the directivity of the antenna at a high speed.
An antenna apparatus according to a first aspect of the present invention comprises a primary radiation element for radiating a radar wave and a dielectric lens for focusing a radar wave, wherein the primary radiation element is movable within the focal plane of the lens.
The change of the position with respect to the lens of the primary radiation element causes the directivity of a radar beam radiated from the primary antenna apparatus to vary. Since the primary radiation element is relatively light-weight, an element driving apparatus may be of a small scale. Further, since the inertia of the primary radiation element is small, it is possible to move the primary radiation element at a high speed, making high-speed scanning of the radar beam possible.
In an antenna apparatus according to another aspect of the present invention, the direction of the center axis of the dielectric lens with respect to the radiation plane of the primary radiation element is variable.
In an antenna apparatus according to still another aspect of the present invention, in order to displace the position of the primary radiator within the focal plane of the dielectric lens, the primary radiator comprises a first dielectric line serving as an input/output section, a dielectric resonator which is coupled to the first dielectric line, and an opening section from which an electromagnetic wave is radiated or is made to enter in the axial direction, a second dielectric line is provided close to the first dielectric line in order to form a directional coupler, and the relative positional relationship between the dielectric lens and the primary radiator is changed in the coupled section of the first and second dielectric lines. Since a movable section which inputs and outputs signals to and from the primary radiator as described above is formed of a directional coupler formed of a dielectric line on the primary radiator side and another dielectric line, it becomes possible to change the relative position between the primary radiator and the dielectric lens while maintaining the coupling relationship.
In the directional coupler, if the amount of coupling is made approximately 0 dB, transmission loss in the directional coupler is suppressed by as much as possible, and the efficiency of the antenna is not reduced.
Further, in the antenna apparatus of the present invention, a transmission section, a receiving section, and a circulator for separating a transmission signal and a received signal are connected to the second dielectric line so that the antenna apparatus is used for both transmission and reception. As a result, the primary radiator formed of the first dielectric line and the dielectric resonator coupled to the first dielectric line, and a second dielectric line coupled to the first dielectric line can be used for both transmission and reception, thereby preventing a larger size because the movable section is formed by using the directional coupler.
Furthermore, in the present invention, a driving section for changing the relative positional relationship between the dielectric lens and the primary radiator may be provided so that a transmission and receiving apparatus is formed. As a result, a small transmission and receiving apparatus capable of scanning in the orientational direction of the antenna can be obtained.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.